Beware that you'll have to leave the newbie-feel-safe desktop environment and do things in console mode. This is because your X-server (the service that provides your desktop) has to be restarted using the new drivers.
You'll make changes to ensure that your window environment will from now on restart using the nvidia drivers. If you mess up you may not be able to return to your desktop until tour changes have been corrected.
open in your favorite text editor "/etc/X11/xorg.conf". Read the nvidia documentation concerning the changes that should be made in the xorg.conf file: "driver nvidia" and something about dri. In here you'll also be able to set the wheel of your mouse and right monitor settings among other things if you want to. Just read the comments supplied in the file. You'll need the monitor documentation to know your horizontal and vertical refresh rates and a correct size of your desktop. WARNING: don't go trying some refresh rates. You may blow up your monitor.
save your file in your home directory. (you won't be able to overwrite the old file yet). ensure you know the path where this file is located and the downloaded nvidia driver.
open a console and type:
mv /etc/X11/xorg.conf /etc/X11/xorg.conf_old
cp /home/[USERNAME]/xorg.conf /etc/X11/xorg.conf
in order to install the driver you'll have to exit your window system. safe all your changed documents now. then:
They'll guide you through the installation. If they complain that the driver is incompatible with an installed driver (NOT an module) then revert (see below). You'll have to recompile your kernel in that case. That will require some knowledge of your computers intestines however.
Return to your window system:
init 4 or init 5 to return to your window system (depending on your distribution). If your screen doesn't return you can revert
hit ctrl+alt+F1, ctrl+alt+F2, ctrl+alt+F3, ... until a console where you can login returns. type
mv /etc/X11/xorg.conf_old /etc/X11/xorg.conf
now try to return to your window system as described. That should work.